Four years after buying the sea rock it lived in, redditor GCS_3 discovered that he had a bobbit worm in his saltwater aquarium. That explained why some of his fish had mysteriously disappeared. In the wild, bobbit worms can grew to almost ten feet in length, although the average is about a yard long. This one was measured at eight inches, after it was "euthanized." The consensus is that it should have been nuked from orbit. See more pictures of this scary worm at imgur. Link

Not something I really expected to see on my lunch break, but once I saw it, I figured I might as well look the damn thing up.

Highlights from Wiki (http://en.wikipedia.org/wiki/Eunice_aphroditois):Eunice aphroditois, the Bobbit worm, is an aquatic predatory polychaete worm dwelling at the ocean floor. This organism buries its long body into an ocean bed composed of gravel, mud or corals, where it waits patiently for outside stimulus to reach one of its five antennae. Armed with sharp teeth, it is known to attack with such speeds that its prey is sometimes sliced in half. Although the worm hunts for food, it is omnivorous. It is also covered in bristles that are capable of a sting that results in permanent numbness in humans.[1] Little is known about the sexual habits and life span of this worm, but researchers hypothesize that sexual reproduction occurs at an early stage, maybe even when the worm is about 3.9 in in length; this is very early, considering that these worms can grow to sizes of nearly 9.8 ft in some cases (although most observations point to a much lower average length of 3 ft 3 in) and an average of 0.98 in in diameter. A long lifespan may very well explain the size of these creatures. Eunice aphroditois is found in warmer oceans around the world, including the Indo-Pacific and Atlantic.[2]